The present invention relates to a polyester monofilament for making endless fabrics and to wear-resistant endless fabrics having arranged therein a polyester monofilament. In particular, the present invention relates to a wear-resistant paper making fabric.
Conventional endless fabrics include many fabrics used for such purposes as a belt conveyor, a dehydration conveyer, a filtration fabric, a power transmitting belt, a dryer canvas for paper making, a felt for paper making or a fabric for paper making. All of these endless fabrics have problems in that they extend in the warp direction and shrink in the weft direction. That is, the fabrics draw up in length while shrinking in width because of the strong tensile force in the warp direction exerted in actual use. Further, the fabrics known in the art are poor in attitude stability because they also draw up in length while shrinking in width with loading in the vertical direction. Furthermore, they also have a problem in that they are required to have a large resistance to wear because they are worn away by contact with the driving rolls or controlling rolls of the machinery during running. They are also required to have a smooth running surface for smooth running and a flat upper surface for carrying something on the fabric. These problems are common to endless fabrics, however, satisfactory countermeasures have not hitherto been found for solving the problems. The present invention has successfully solved these problems.
The aforementioned requirements are especially important for making endless fabrics for the paper making industry. Fabrics for paper making are also required to have properties to be described hereinafter which are unique to paper making in addition to the aforementioned properties. The description of the common problems described above referring to fabrics for paper making will clarify problems common to most endless fabrics and solutions to the problems. Thus, the present invention is described with reference to fabrics for paper making as a typical example.
There have hitherto been set out many requirements in addition to the aforementioned problems for fabrics for paper making. These problems are roughly classified into:
(a) problems relating to the quality of paper for its own sake such as the prevention of wire marks or satisfactory intertwinement of paper fibers or problems of yields in paper making; PA1 (b) the improvement of the resistance to wear or the extension of the working life of a fabric; PA1 (c) problems of good water drainage property. PA1 (1) According to known melting yarn making techniques, the filament is extruded from the conventional yarn making nozzle. PA1 (2) Then the yarn is stretched at 80.degree. to 100.degree. C. to a stretch degree of 2 to 4. PA1 (3) The resulting monofilament, after heat setting if desired, has the physical characteristics described herein. Heat setting is not necessary in the case where the resulting monofilament already has the physical characteristics described. In other words, the physical characteristics of monofilament vary in accordance with degree of polymerization for polyester, yarn making conditions, stretching degree, stretching temperature, and so on. Therefore, heat setting can be carried out if necesssary.
These problems relate to each other in many points; i.e., the problems of: (a) being closely related to the structure of the paper making surface of the fabric, (b) being related to the structure of the running surface of the fabric, and (c) being related to the whole fabric.
There have hitherto been proposed many solutions to problem (a). Nevertheless, there have not been investigations sufficient to avoid problem (b), that is, the improvement of the resistance to wear of fabrics for paper making; the only exception being of preventing the warp from excessive wear by making the paper making fabric with a running side of the weft wearing type. In recent years, there have been increased requirements such as the increase in the rate of paper making, the increase of the amount of loading fillers or the increasing necessity of producing neutral paper, and thus the resistance to wear of the fabric for paper making becomes an issue.
In general, endless fabrics including fabrics for paper making desirably have the wear resistant weft on the running surface taking into consideration the attitude stability of the fabric in use and the extension of its working life. This is because the wearing of the warp causes a change in the size of the fabric and finally the break of the warp which further causes the direct break of the fabric itself, so that a paper making fabric of a warp wearing type has a short working life.
For the purpose of improving the resistance to wear, a polyamide yarn having resistance to wear has been conventionally employed. However, such an attempt did not change the substantial structure of the fabric but only utilized the properties of a material to be used, and thus any epoch-making advantageous effects could not be expected from the fabric. On the other hand, a disadvantage of poor attitude stability was found in fabrics for paper making composed of a polyamide yarn.
Therefore, paper making fabrics which were less extendable and excellent in attitude stability were conventionally constructed by using a polyester yarn having an excellent rigidity as either a warp and a weft.
Also, in such conventionally used fabrics for paper making, a yarn having a large diameter was used as a weft on the running side of the fabrics for paper making in order to satisfy the aforementioned requirements. Such an attempt was successful to a certain extent in the improvement in the resistance to wear. However, such an attempt led to an imbalance between the weft and the warp because of the larger diameter of the weft. Thus, too many disadvantages were present to be used in practice such as the deterioration of the crimping ability or the appearance of wire marks.
Furthermore, as is understood from the aforementioned problem (c), the water drainage property is also affected by the change of the structure of a fabric, and problems will not be solved by such temporary means as using a large diameter yarn.
In view of such conventional technical problems, the present inventors have invented a special, extendable and heat shrinkable polyester monofilament which is excellent in resistance to wear, attitude stability and surface smoothness effect for the construction of an endless fabric; improved the structure of an endless fabric for paper making with use of the filament to improve the resistance to wear; and also improved the performance in making paper with respect to the water drainage property and the wire-marking property.